Basically, volumetric efficiency concerns how efficiently air flows through the engine and is the ratio of measured flow to theoretical flow. On a normally aspirated engine this is not going to be 100% because of several factors. The more obvious of these are the resistance to air flow offered by the air filter, valves and ducting coupled with the back pressure etc from the exhaust system.
The torque app calculates volumetric efficiency and so, just like the MAF data, I plotted this against engine revolutions.
This was the data before cleaning the MAF meter. (Note: at approximately 2500 rpm the turbo begins to provide boost. At approximately 1800rpm, I think, the EGR valve should be closed and therefore the MAF meter is reading all of the air flow into the engine.)
And this after cleaning
It clearly demonstrates the effect of cleaning the MAF! Why is the improvement so much more noticeable on this data than the simple MAF figures? I'm not quite sure but air flow temperature and manifold pressure are used in the calculations and these might now be measuring more accurately as well.
One thing that does surprise me is that a 100% wasn't reached. My surprise is because the engine has a turbo charger and so the air is being forced through the engine which will tend to negate the air flow resistance mentioned earlier. So could this mean the MAF meter is reading low? That would be consistent with information I have read on the most common characteristic of a faulty MAF meter. Perhaps some readings taken whilst driving may be useful. (The above and earlier graphs are based on data obtained with the car stationery).
